Interactions of transition-metal ions with flavins, in both singlet and triplet excited states, are under investigation. Experimental techniques employed in this research include fluorescence quenching (measured by both intensity and decay-time techniques), time-resolved fluorescence spectroscopy, flash photolysis, and phosphorescence spectroscopy. The use of fluorescence quenching data to determine formation constants for ground-state complexes of flavin with metal ions in solution is also under scrutiny. Luminescence and photochemistry of metal complexes of flavoquinones and flavosemiquinones in aqueous solution will also be examined. The ultimate objective of this research is to characterize, as completely as possible, the interactions of the various redox states of flavins with metal ions, and to do so for both the ground and electronically excited states of the flavin. These results should assist in clarifying the role of flavin-metal interactions in metal-containing flavoproteins, and should also contribute to increased understanding of the role of flavin excited states in photobiological phenomena.